拦污栅条一般常用所面形状有哪几种？
参考答案：
一般常用断面形状有四种：
迎水面和背水面加工圆形，迎水面加工圆形，矩形，圆形。
----Who’s the man sitting under the tree? ----I don't ___ this man, but I’ve ___ him.
A．know of, heard about
B．know, heard about
C．know, heard
D．know of, heard
X.25物理层采用哪些CCITT接口标准？
